motion_est/producer_slowmotion.c: check for null pointer
motion_est/producer_slowmotion.c: check for null pointer

Fixes Coverity CID 709401: Dereference before null check (REVERSE_INULL)
Directly dereferencing pointer "frame".
279        *frame = mlt_frame_init( MLT_PRODUCER_SERVICE( this ) );
280
281        mlt_properties properties = MLT_PRODUCER_PROPERTIES(this);
282
283
Dereferencing "frame" before a null check.
284        if( frame != NULL )

siddharudh/mlt,gmarco/mlt-orig,anba8005/mlt,mltframework/mlt,wideioltd/mlt,anba8005/mlt,j-b-m/mlt,mltframework/mlt,siddharudh/mlt,zzhhui/mlt,wideioltd/mlt,zzhhui/mlt,j-b-m/mlt,gmarco/mlt-orig,anba8005/mlt,anba8005/mlt,zzhhui/mlt,xzhavilla/mlt,zzhhui/mlt,mltframework/mlt,anba8005/mlt,siddharudh/mlt,mltframework/mlt,zzhhui/mlt,j-b-m/mlt,gmarco/mlt-orig,j-b-m/mlt,mltframework/mlt,gmarco/mlt-orig,mltframework/mlt,siddharudh/mlt,wideioltd/mlt,anba8005/mlt,j-b-m/mlt,siddharudh/mlt,j-b-m/mlt,mltframework/mlt,wideioltd/mlt,anba8005/mlt,wideioltd/mlt,anba8005/mlt,xzhavilla/mlt,mltframework/mlt,gmarco/mlt-orig,j-b-m/mlt,xzhavilla/mlt,xzhavilla/mlt,gmarco/mlt-orig,xzhavilla/mlt,j-b-m/mlt,zzhhui/mlt,zzhhui/mlt,xzhavilla/mlt,xzhavilla/mlt,j-b-m/mlt,siddharudh/mlt,zzhhui/mlt,anba8005/mlt,gmarco/mlt-orig,wideioltd/mlt,xzhavilla/mlt,wideioltd/mlt,mltframework/mlt,siddharudh/mlt,j-b-m/mlt,gmarco/mlt-orig,gmarco/mlt-orig,wideioltd/mlt,siddharudh/mlt,mltframework/mlt,siddharudh/mlt,wideioltd/mlt,xzhavilla/mlt,zzhhui/mlt